<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div class="page-var-demo" id="page-var-demo">
    <!--class="page-var-demo"用来设置样式；id="page-var-demo"用给JS用；-->
    <div class="btns-groulp">
        <a href="javascript:;" class="xxxx xxxxx j-open-demo" data-demo_id="456465465">打开演示窗口</a>
        <!--j-open-demo 这些是给JS用来触发某些事件用的，data-demo_id用来储存需要的值的-->
        <a href="javascript:;" class="xxxx xxxxx j-set-demo">设置演示数据</a>
    </div>
</div>
<script>
    var name="朱安邦",
        gender;
    console.log(name,typeof name);      //朱安邦 string
    console.log(gender,typeof gender);  //undefined "undefined"
</script>
</body>
</html>